Mechanisms with interesting force-deflection characteristics have always intrigued engineers and scientists and thus have been a subject of on-going research. Mechanisms using linear springs to give increased force outputs with greater input displacements have been widely known and researched. In some applications, the output force may be desired to stay constant with a change in the input displacement. Such situations arise in applications such as robotic grasping, preventing damage to machine tools or end-effectors due to unforeseen position errors, biomedical applications, haptic devices, and micro-grasps. These mechanisms are referred to as “constant-force” mechanisms. An exemplary constant force-mechanism is described in U.S. Pat. No. 5,649,454 (Midha et al.), its contents are expressly incorporated herein by reference.
A constant-force mechanism is designed to produce a constant-force for the entire range of motion. This mechanism is a compliant mechanism as it gains movement from parts that flex, bend, or have a resiliency and in addition produces a desired constant-force output at all times. A constant force can be generated using hydraulic, pneumatic, and electrical device units, or even with a negator spring. But, from practical design considerations for micro applications, these solutions may not be possible. For micro applications, a solution applicable to a mechanical linkage system is needed which does not incorporate a power source.
Accordingly, it would be more useful to engineers and scientists alike if the constant-force output could be adjusted and that it has micro scale applications. Accordingly, there is a need for a variable or adjustable constant-force mechanism for increased versatility and one which has a number of different applications including micro-scale applications.